Resistor bulb



June 12, 1956 H. VOORMAN, JR

RESISTOR BULB Filed Oct. 26, 1955 INVENTOR HHII ATTORNEYS United StatesPatent O "fic Rnsisron BULB Henry Voorman, Jr., Livingston, N. J.,assignor to Weston Electrical Instrument Corp., Newark, N. J., acorporation of New Jersey Application October 26, 1953, Serial No.388,098

9 claims. (ci. 24u-ss) This invention relates to resistor bulbs suchl asemployed in the electrical measurement of temperature, and moreparticularly to resistor bulbs of the type in which 'the resistance wireis wound upon a metal tube that is housed within the hollow stem of amounting head which rovides a socket for receiving a terminal plugconnector.

A resistor bulb of the general type stated is disclosed in Patent No.2,149,448, issued March 7, 1939, on an application filed by K. M.Lederer and Alexander Dempster, and the mechanical construction thereillustrated and described has proved quite satisfactory but is expensiveto manufacture.

Objects of the present invention are to provide resistor bulbs whichinclude a lesser number of parts and which are more readily and moreeconomically manufactured than the prior resistor bulbs of the samegeneral type. More specifically, an object of the invention is toprovide a resistor bulb which comprises three main components; namely, amounting head that includes a hollow stem for housing the resistancewire, a bushing of insulating material to which is secured an anodizedaluminum tube carrying the resistance wire and which is provided withtwo longitudinal openings for connecting wires, and a pre-formed socketcup for insertion in the mounting head, the socket cup includingglass-sealed terminal pins to which the connecting wires are soldered. Afurther specific object is to provide a resistor bulb in which all ofelectrical connections are soldered or welded.

These and other objects and the advantages of the invention will beapparent from the following specification when taken with theaccompanying drawings in which:

Fig. l is an elevation, with parts broken away, of a resistor bulbembodying the invention;

Fig. 2 is a fragmentary central section, on an enlarged scale, throughthe stem of the resistor bulb and showing the relative arrangement ofthe resistance wire, its support and insulation;

Fig. 3 is a perspective view on an enlarged scale of the insulatingbushing which is an important element of the resistor bulb;

Fig. 4 is a fragmentary central section of a modified form of terminalsocket cup; and

Fig. 5 is a fragmentary section on line 5-5 of Fig. 4.

In the drawings, the reference numeral 1 identifies a thin aluminum tubein which a helical groove 2 is rolled or pressed to receive a winding ofbare resistance wire 3 in the form of a closely-wound helical coil ofsmall diameter and small pitch, the tube being anodized or covered withan integral layer 4 of insulating oxide. The tube may be provided withparallel notches 5, or an integral detent, at the bottom so that thewinding may be looped back upon itself to place both terminals of thewinding 3 at the upper end of the tube. The upper 'end of the supportingtube is slipped over and cemented to the lower end of a ceramic bushing6, preferably of steatite, having an enlarged diameter head 7 throughwhich openings 8 extend longitudinally to receive connecting wires 9.The bushing 6 is provided with longi- 2,750,4@3 Patented .lune 12, 1956tudinal scores or slots lt) below the head 7 and in line With theopenings 8 to receive the connecting Wires 9 which are retained in placeby a high-temperature cement 11. Notches 12 are cut into the bushing 6from opposite sides to intersect the slots 10 and thus make the lowerends of the connecting wires 9 available for connection, preferably madeby silver soldering or spot welding, to the upper ends of the resistancewire 3.

'The connecting wires 9 pass upwardly through hollow terminals 13, 13which extend through and are insulated by glass beads 14, 14 from apre-formed cup 15, made of iron or other suitable metal and preferablycadmium plated to resist corrosion; the upper ends of the connectingwires 9 being anchored to the terminals 13 by solder 16 in the mannerwhich is customary with the terminal connections of electron tubes. Analinement projection 17 is formed on the inner surface of the cup 15 forthe proper positioning of a cable connector, not shown, for makingelectrical connection to the resistor bulb.

The mounting head of the resistor bulb includes a hollow stem 18, closedat its lower end, and welded into the lower threaded end 19 of a bushinghaving a hexagonal section 20 for receiving a wrench by which thethreaded section 19 may be introduced into a correspondingly threadedopening in the water jacket or oil case of an engine, into the wall of acarburetor air inlet, or into any other object or lluid container wheretemperature measurements are to be made.

As shown in Figure 2, the groove 2 of the anodized aluminum tube 1 is ofgreater depth than the diameter of the single layer helix of resistancewire 3 and a coating of insulating enamel 2l is applied over the Windingwithin the helical groove. For further insurance against any shorting ofthe resistance wire upon the stem 18 of a resistor bulb, a thread ofglass liber 22 is wound over the resistance Wire and preferably iscontinued upwardly to the head '7 of the bushing 6, thus securelyanchoring the resistance wire to the aluminum support and the connectingwires to the bushing 6.

After applying this insulation, the assembly is slipped, as shown inFig. l, into the mounting head and silver solder 23 is applied along themutual peripheral surfaces of the pre-formed cup 1:3' and the mountingbushing to form a water-tight joint.

In a modified construction, as shown in Fig. 4, solid pin terminals 13are employed in the cup 15 in place of hollow pin terminals, thusavoiding the inconvenience of making soldered connections to the upperends of hollow pin terminals which are located somewhat below the toplevel of the cup 15. In the modified construction, the connecting wires9 are spot welded to the bottoms of the terminal pins 13.

From the above description of my invention, it will be apparent that aresistor bulb made in accordance therewith includes a greatly-reducednumber of component parts and does not require close tolerances eitherin the production of the parts or their assembly. The bulb ishermetically-sealed yet the sub-assembly unit, comprising the pre-formedcup, ceramic tube and resistance wire, can be removed from the mountingsocket by applying heat to the rim of the cup, thereby facilitating thereplacement of a damaged unit. Such unitary subassembly arrangement alsofacilitates the production of the bulbs since all adjustments and testscan be performed prior to insertion of the sub-assembly into themounting socket.

Having now described my invention in detail in accordance with thepatent statutes what I desire to protect by Letters Patent ot' theUnited States is recited in the following claims.

I claim:

l. A resistor bulb for the electrical measurement of temperaturecomprising a mounting head having an axial bore therethrough, a metalcup seated within the outer portion of said bore and having its rimmechanically secured and sealed to the adjacent peripheral edge of saidmounting head, a pair of contact pins extending through the bottom wallof said cup and insulated therefrom, a bushing of insulating materialhaving a pair of wires extending therethrough, a metal tube secured toand axially of the inner end of said bushing, a winding of resistancewire on and insulated from said tube, and soldered connections betweenthe ends of said pair of wires and respectively said contact pins andsaid resistance wire.

2. A resistor bulb as recited in claim l wherein said metal cupconstitutes a socket for receiving a terminal plug having contacts forengagement with said contact pins, and said cup is provided with alongitudinal indentation for alinement of the terminal plug within saidsocket.

3. A resistor bulb comprising a helically grooved and anodized aluminumtube, a winding of helically coiled resistance wire within the helicalgroove of said tube and spaced from the cylindrical surface deiined byouter edges of said grooved tube, an insulating bushing having an outercylindrical head and an inner cylindrical stem extending into the outerend of said tube to support the same, said bushing having a pair ofopenings therethrough, connecting wires extending through said openingsand having their inner ends soldered to the respective ends of saidresistance wire, a socket cup of sheet metal having a pair of contactpins extending through and insulated' from the bottom wall of saidsocket cup, soldered connections between the outer ends of saidconnecting wires and said contact pins, a mounting head having an axialbore therethrough, and means hermetically sealing the rim of said socketcup to the outer end of said bore of the mounting head.

4. A resistor bulb as recited in claim 3, wherein the inner stem of saidinsulating bushing is of less diameter 4 than the outer cylindrical headthereof, said openings extend through the head of the bushing and alinewith diametrically arranged longitudinal grooves in the inner stem, incombination with cement retaining said connecting wires in saidlongitudinal grooves.

5. A resistor bulb as recited in claim 4, wherein said inner stem isprovided with longitudinally spaced notches intersecting the respectivegrooves at the opposite sides thereof to expose the inner ends of saidconnecting wire for convenience in establishing said solderedconnections.

6. A resistor bulb as recited in claim 3, wherein said mounting headincludes an inner hollow stem for housing said metal tube and theresistance wire thereon, in combination with a coating of insulatingenamel upon the resistance wire within the groove of said metal tube,and a winding of glass ber thread over said enamel coating and withinthe helical groove of said metal tube.

7. A resistor bulb as recited in claim 6 wherein said winding of glassber thread extends beyond the outer end of said metal tube and coversthe stern of said insulating bushing.

8. A resistor bulb as recited in claim 3, wherein said contact pins arehollow and said connecting wires extend through the same, in combinationwith solder uniting the upper ends of said contact pins and saidconnecting wires.

9. A resistor bulb as recited in claim 3, wherein said contact pins aresolid and said connecting wires are united to the same below said socketcup.

References Cited in the tile of this patent UNITED STATES PATENTS2,149,448 Lederer et al. Mar. 7, 1939 2,476,099 Knudsen July 12, 19492,590,041 Roost Mar. 18, 1952

